Field of the Invention
Embodiments of the present invention relate generally to a method for correcting a drift of an accelerating voltage, method for correcting drift of a charged particle beam, and a charged particle beam writing apparatus, and more specifically, relate to a method for correcting drift of an accelerating voltage applied to a beam source of an electron beam writing apparatus, for example.
Description of Related Art
The lithography technique that advances miniaturization of semiconductor devices is extremely important as a unique process whereby patterns are formed in semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. For forming a desired circuit pattern on such semiconductor devices, a master or “original” pattern (also called a mask or a reticle) of high accuracy is needed. Thus, the electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for producing such a high-precision master pattern.
FIG. 10 is a conceptual diagram explaining operations of a variable-shaped electron beam writing or “drawing” apparatus. The variable-shaped electron beam (EB) writing apparatus operates as described below. A first aperture plate 410 has a quadrangular aperture 411 for shaping an electron beam 330. A second aperture plate 420 has a variable shape aperture 421 for shaping the electron beam 330 having passed through the aperture 411 of the first aperture plate 410 into a desired quadrangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the aperture 411 is deflected by a deflector to pass through a part of the variable shape aperture 421 of the second aperture plate 420, and thereby to irradiate a target object or “sample” 340 placed on a stage which continuously moves in one predetermined direction (e.g., the x direction) during writing. In other words, a quadrangular shape that can pass through both the aperture 411 of the first aperture plate 410 and the variable shape aperture 421 of the second aperture plate 420 is used for pattern writing in a writing region of the target object 340 on the stage continuously moving in the x direction. This method of forming a given shape by letting beams pass through both the aperture 411 of the first aperture plate 410 and the variable shape aperture 421 of the second aperture plate 420 is referred to as a variable shaped beam (VSB) system.
In the writing apparatus, electron beams are emitted by applying an accelerating voltage to the cathode of the electron gun from a high voltage power source. Due to the high voltage power source, drifts may occur in the accelerating voltage with the passage of a long period of time although they are minute variations in the range of specification values. It is reported that the beam irradiation position deviates by variation of the accelerating voltage, etc. (e.g., refer to Re-publication of PCT International Application No. 2009/136441). Since the accelerating voltage in which drifts occur is a high voltage, it has been difficult to highly accurately measure a minute variation of the accelerating voltage during an operation of the writing apparatus. Therefore, there has been a problem in that it is difficult to correct a minute drift itself of the accelerating voltage. Accordingly, the writing accuracy is conventionally maintained by correcting beam variations due to drifts in the accelerating voltage by periodically performing various types of beam adjustment, instead of correcting the drift itself of the accelerating voltage. However, it takes a long time to make various beam adjustments that are executed based on a plurality of adjustment items, thereby affecting the throughput of the writing apparatus.